The present invention relates to an apparatus for clamping substrates during a semiconductor die attach process. The present invention has particular applicability in die bonding semiconductor devices to thin laminated substrates.
Certain conventional fine-pitched ball grid array (FBGA) packaging schemes for semiconductor devices employ a substantially flat, rigid, multi-layer laminated substrate comprising gold tracers embedded in an organic resin, such as bismaleamide triazine (xe2x80x9cBT resinxe2x80x9d). Bare semiconductor devices, known as xe2x80x9cdiesxe2x80x9d, are attached to the substrate with epoxy, such as in a stacked die configuration, in a process known as xe2x80x9cdie bondingxe2x80x9d. Wires are attached between the dies and the substrate in a wire bonding operation, and the dies are then encapsulated, as by molding. Solder balls are thereafter attached to bonding pads on the underside of the substrate, and the packaged devices are singulated, tested and marked.
During the die bonding operation, a die is picked up, typically by an automatic pick-and-place die bonding head, and placed in a precise location on the substrate using a relatively small amount of pressure (e.g., about 150-200 grams). The die bonding operation requires the substrate to be heated to about 100-175 degrees Centigrade. Heating is typically performed via a heater block in the bed of the die bonding machine before and during die bonding.
However, the substrate, typically formed as a strip about 5 mm wide and about 190 mm long, tends to warp at the elevated die bonding temperature, preventing precise positioning of the die on the substrate. This imprecise die positioning results in lower yields and increased production costs. Conventional die bonders use vacuum to hold the substrate down against the bed and the heater block, but the substrate typically detaches from the vacuum holes in the bed when it warps. Thus, the use of vacuum to hold down the substrate is not effective to reliably prevent substrate warpage.
There exists a need for a die bonding apparatus for assembling thin substrate packages without substrate warpage, thereby reducing manufacturing costs and increasing production throughput.
An advantage of the present invention is a die bonding apparatus that prevents warpage of substrates before and during the die bonding procedure.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a clamp for clamping a substantially flat substrate to a bed of a processing machine, the clamp comprising a clamp body; a plurality of rollers for contacting a pair of opposing outer edges of the substrate and allowing the substrate to move along a longitudinal axis of the bed when the substrate is clamped to the bed; and a plurality of resilient fingers, each finger being attached to the clamp body and one of the rollers, for urging the roller against the substrate to prevent warpage of the substrate.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.